Audio Streams Over Peripheral Component Interconnect (pci) Express (pcie) Links

1. A method for synchronizing clocks across a point-to-point serial bus interface, the method comprising: determining a time offset between a host clock and a device clock in part by acquiring a command receipt time from a device associated with the device clock and storing an initial time at a host associated with the host clock; and adjusting the host clock by the time offset when sending audio data to the device.

2. The method of claim 1 , wherein the point-to-point serial bus interface comprises a peripheral component interconnect (PCI) express (PCIE) bus interface.

3. The method of claim 1 , wherein the host that includes the host clock comprises an application processor.

4. The method of claim 1 , wherein the device comprises a modem.

5. The method of claim 1 , wherein determining the time offset further comprises sending a command to the device.

6. The method of claim 5 , wherein acquiring the command receipt time from the device further comprises acquiring a write command receipt time from the device.

7. The method of claim 6 , wherein acquiring the write command receipt time comprises reading a register in the device.

8. The method of claim 6 , wherein acquiring the write command receipt time comprises receiving the write command receipt time pushed from the device.

9. The method of claim 5 , wherein determining the time offset further comprises considering jitter.

10. A method of maintaining synchronization between a modem and an application processor over a peripheral component interconnect (PCI) express (PCIE) link, the method comprising: receiving a posted command at a device over a point-to-point serial bus interface; storing a request identifier and a time source in a first register within a memory mapped input/output (MMIO) at the device; responsive to receiving the posted command, storing a local time in a second register within the MIMO at the device; and providing the local time to a host.

11. The method of claim 10 , wherein providing the local time to the host comprises providing the local time responsive to a read command from the host.

12. The method of claim 10 , wherein providing the local time to the host comprises pushing the local time to the host.

13. An apparatus comprising an application processor comprising: a point-to-point serial bus interface; a host clock; and a modem host interface operatively coupled to the point-to-point serial bus interface and the host clock and configured to: determine a time offset between the host clock and a clock at a device in part by acquiring a command receipt time from a device associated with the device clock and storing an initial time; and adjust the host clock to maintain synchronization between the host clock and the clock at the device.

14. The apparatus of claim 13 , wherein the point-to-point serial bus interface comprises a peripheral component interconnect (PCI) express (PCIE) bus interface.

15. The apparatus of claim 13 , further comprising a register configured to store the initial time associated with the host clock.

16. The apparatus of claim 13 , wherein the modem host interface is further configured to send a write command to the device.

17. The apparatus of claim 16 , wherein the command receipt time comprises a write command receipt time associated with the write command from the device.

18. The apparatus of claim 13 , further comprising an integrated circuit (IC).

19. The apparatus of claim 13 , further comprising a device selected from the group consisting of: a set top box; an entertainment unit; a navigation device; a communications device; a fixed location data unit; a mobile location data unit; a global positioning system (GPS) device; a mobile phone; a cellular phone; a smart phone; a session initiation protocol (SIP) phone; a tablet; a phablet; a server; a computer; a portable computer; a mobile computing device; a wearable computing device; a desktop computer; a personal digital assistant (PDA); a monitor; a computer monitor; a television; a tuner; a radio; a satellite radio; a music player; a digital music player; a portable music player; a digital video player; a video player; a digital video disc (DVD) player; a portable digital video player; an automobile; a vehicle component; avionics systems; a drone; and a multicopter, wherein the application processor is integrated into the device.

20. An apparatus comprising a first device comprising: a point-to-point serial bus interface; a memory mapped input/output (MMIO) comprising: a first register; and a second register; and a modem host interface operatively coupled to the point-to-point serial bus interface and configured to: receive a posted command from a host; store a request identifier and a time source in the first register; responsive to receiving the posted command, store a local time in the second register; and provide the local time to the host.

21. The apparatus of claim 20 , wherein the modem host interface is configured to provide the local time to the host responsive to a read command from the host.

22. The apparatus of claim 20 , wherein the modem host interface is configured to push the local time to the host.

23. The apparatus of claim 20 , further comprising an integrated circuit (IC).

24. The apparatus of claim 20 , further comprising a second device selected from the group consisting of: a set top box; an entertainment unit; a navigation device; a communications device; a fixed location data unit; a mobile location data unit; a global positioning system (GPS) device; a mobile phone; a cellular phone; a smart phone; a session initiation protocol (SIP) phone; a tablet; a phablet; a server; a computer; a portable computer; a mobile computing device; a wearable computing device; a desktop computer; a personal digital assistant (PDA); a monitor; a computer monitor; a television; a tuner; a radio; a satellite radio; a music player; a digital music player; a portable music player; a digital video player; a video player; a digital video disc (DVD) player; a portable digital video player; an automobile; a vehicle component; avionics systems; a drone; and a multicopter, wherein the first device is integrated into the second device.